1. Field of the Invention
The present invention relates to a torque limiting wrench, and more particularly to a torque limiting wrench having a marking mechanism which marks a part when the part has been manipulated to a desired level of torque.
2. Description of Related Art
Torque limiting wrenches have applications in various manufacturing environments where application of a consistent level of torque is needed. There are numerous reasons for desiring consistency in application of torque in a manufacturing process, such as avoiding localized stressing of parts and assuring full tightening of fasteners. Application of too great a torque or over tightening in assembling a fastener can cause the fastener to fail, thus torque limiting wrenches such as U.S. Pat. Nos. 4,393,734, 3,523,471 and 3,667,327 have been developed and are well known in the art. Further, however, it is important for fasteners to be properly tightened through application of a specified amount of torque.
It would be desirable for a manufacturing quality inspector to be able to visually check the level of torque applied to fasteners in a manufacturing environment. My previous patent, U.S. Pat. No. 4,393,734, herein incorporated by reference, discloses an invention which provides this inspection capability. This invention uses a pneumatic line to create pressure in a torque limiting wrench housing when the desired level of torque is reached. This pressure causes an ink-marking unit to slide toward the part and create a visible mark for visual confirmation that the fastener has been properly "torqued" (assembled with the appropriate torque).
There are several limitations of my previous invention. The attachment of a pneumatic line may limit the functional use of a tool in a manufacturing environment. It may also be difficult, cumbersome and costly to provide pneumatic lines to certain locations in a manufacturing facility or assembly line. In addition, the attachment of these pneumatic lines may limit the travel of the unit, i.e., the ability of the user to walk around and perform work in areas where work space is limited, areas where pneumatic lines are unavailable, or outside.
Another limitation with my previous invention is the inefficiencies of the metal-tipped striking pins. Large pneumatic line pressures are required in order to sufficiently force the striking pin against the part to mark the part. Further, there is only the physical mark to verify proper torque.
Therefore, it would be desirable to develop a combined electronic torque limiting and marking wrench which does not have the previously mentioned limitations.